On Establishing Buckling Knockdowns for Imperfection-Sensitive Shell Structures*

This presentation contributes to recent efforts aiming to revise long-standing knock-down factors for elastic shell buckling, which are widely regarded as overly conservative for well-constructed shells. The presented work focuses on cylindrical shells under axial compression with emphasis on the role of local geometric dimple imperfections and the use of lateral force probes as surrogate imperfections. Two buckling thresholds are identified (local and global buckling) and related for the two kinds of imperfections. Four sets of relevant boundary conditions are accounted revealing a strong dependence of the global buckling load on overall end-rotation constraint when local buckling precedes global buckling. A reasonably complete picture emerges, which should be useful for informing decisions on establishing knockdown factors.